Dual treatment of asbestos fibers

ABSTRACT

Treatment of asbestos fiber with a first coating of at least about 0.4 percent by weight of alkali-metal silicate solids or colloidal silica, and subsequent distribution of a non-foaming anionic dispersant on the coated fiber produces an asbestos fiber product that possesses improved filtration properties. The fiber product improves the production rate of articles from asbestoscement slurries or pastes and eliminates the loss in strength of asbestos-cement articles that usually results from inclusion of silicate-treated fibers in the slurries or pastes.

States Patent [191 EJHQ Sadler Feb. 6, 1973 l DUAL TREATMENT OF ASBESTOSFIBERS [75] Inventor: Thomas Harry Sadler, Belle Mead.

1969, abandoned.

[52] U.S.CI. ..l17/70 S, 117/70 R, 117/126 AQ, 117/126 AF, 162/153,162/154 [51] Int. Cl. ..B44d 1/16 [58] Field of Search 17/126 A0, 126AF, 169 A, 117/169 R, 70 R, 69; 162/154, 155

[56] References Cited UNITED STATES PATENTS 3/1965 Pundsack et aI.162/154 4/1940 Badollet ..l62/l55 FOREIGN PATENTS OR APPLICATIONS1I/l940 Badollet ..l62/l54 H1952 Maxwell ..162/l5$ [[1962 Great BritainPrimary ExaminerAlfred L. Leavitt Assistant Examiner-Cameron K.Weiffenbach Attorney-John A. McKinney, Robert M. Krone, Joseph J. Kellyand Ronald M. Halvorsen [57] ABSTRACT Treatment of asbestos fiber with afirst coating of at least about 0.4 percent by weight of alkali-metalsilicate solids or colloidal silica, and subsequent distribution of anon-foaming anionic dispersant on the coated fiber produces an asbestosfiber product that possesses improved filtration properties. The fiberproduct improves the production rate of articles from asbestoscementslurries or pastes and eliminates the loss in strength ofasbestos-cement articles that usually results from inclusion ofsilicate-treated fibers in the slurries or pastes.

10 Claims, No Drawings DUAL TREATMENT OF ASBESTOS FIBERSCROSS-REFERENCES TO RELATED APPLICATIONS This application is acontinuation-in-part of copending co-assigned application Ser. No.879,549, filed Nov. 24, 1969, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to providing asbestosfibers with improved filtration characteristics, and in particular theinvention is directed to improved methods of treating asbestos fibersand to the improved fibers so produced. While the invention findsparticular use in the manufacture of asbestos-cement articles by thefiltration of particulate materials from a slurry containing asbestosfibers, hydraulic cement, and silica, and in the manufacture ofasbestos-cement pipe using chrysotile as the major fiber component ofsuch a slurry, it is to be understood that in its broader aspects theinvention can be employed in the manufacture of a variety ofasbestos-containing articles.

Asbestos has for some years been employed in a number of common productssuch as asbestos-cement boards, sheets, shingles, pipe, etc,; and paperand millboard which are produced by so-called wet or dry processes thatinclude filtration or percolation-type procedures in which a liquid,typically water, is withdrawn from within a mass or body includingasbestos fibers. Exemplary of such manufacturing procedures is the wetprocess which conventionally involves the steps of forming an aqueousslurry of asbestos fibers and Portland cement in water, flowing theslurry onto a filter element upon which the dispersed solids of theslurry may be collected, removing water in the slurry through the filterelement by filtration, and then removing the formed mass of asbestosfibers and cement from the filter element. Because of inhibition of thefiltering by the asbestos fibers and finely divided cement particles,there are very practical limitations upon the thicknesses of theresulting layers which can be collected on filter elements in thisfashion. Thus, as the collected mass builds up on the filter element,the rate of filtration rapidly decreases, making it impractical toformstructures of any great thickness with a rate of throughput whichmust be obtained in commercial operations.

In a conventional dry process used to form asbestoscement articles, thedry materials, such as asbestos, silica, cement, and pigment are blendedtogether and formed into batches by weight. Sufficient water is added toeach batch to form a plastic paste which can be molded, calendered,pressed or extruded prior to standard asbeStos-cement curing operations.

The filtration properties of chrysotile asbestos fibers differsubstantially with the source or mine location as well as by type, gradeand consistency, ranging from the relatively fast filtering harsh fiberto slow filtering soft fiber. Typical of the latter class of fiber areasbestos materials found in the Quebec, Canada area.

The filtration characteristics of chrysotile asbestos are a significantconsideration in determining the suitability or utility of a particularfiber or fiber blend in wet process and dry process manufacturingprocedures, and these characteristics are particularly decisive in theconventional wet machine processes which are normally employed in theproduction of asbestos-cement pipe, sheets, board, and paper typeproducts, as well as molded or pressed products.

In the past, a large number of treatment methods have been proposed andevaluated to increase the filtration rate of the slower filteringfibers. They include thermal treatment of the fiber; the application ofassorted coatings to the fiber; the use or organic coagulating agentsand inorganicsalt solutions; and soaking in sodium silicate solutionsfollowed by dewatering with an acid treatment to minimize theaccelerating effect of sodium silicate on hydraulic cement. However,notwithstanding the disadvantages entailed in the utilization of theslower filtration fiber in wet machine processes, only a very few ofthese treatment methods for upgrading the filtration characteristics ofasbestos fiber have been extensively adopted. Two of these proceduresare described below.

It has previously been found that a non-foaming anionic dispersant canbe added to a slurry or paste containing asbestos fibers to'increase therate at which water' can be removed from the slurry or paste. While thisprocess has been use commercially and produces the desired results,increased filtration rates, it has been found that the effect of thenon-foaming anionic dispersant is not cumulative. That is, whileincreased filtration rates result from addition of the dispersant up toa certain weight percentage level, once that level is reached, furtheraddition of the dispersant does not result in additional increases inthe filtration rate. Thus, there is an upper limit on the maximumfiltration rate for a given slow-filtering asbestos fiber that isobtainable by this process.

The silicate treatment of asbestos fibers increases filtration rates,but results in considerable decreases in strength of productsincorporating the .treated fiber when large quantities of silicates areadded in an effort to greatly increase filtration rates. A preferredsilicate treatment procedure, which is used commercially but cannonetheless result in asbestos-cement products of decreased strength athigh silicate levels is described in US. Letters Pat. No. 3,173,831.This method of spraying a silicate solution onto asbestos fibers greatlyimproves the filtration characteristics of chrysotile asbestos fiber,but has a strength-decreasing effect on asbestos-cement products. Thus,for practical purposes it is desirable to arrive at a compromise of a0.4 0.6 percent by weight silicate treatment which does help fiberfilterability without a prohibitive decline in product strength. Higheramounts of silicate progressively improved filtration properties, butresulting strength losses make the higher amount of silicateimpractical.

Thus, while the addition of a non-foaming anionicdispersant, or thedeposition of about 0.4 0.6 percent or less by weight of silicatehavebeen used commercially to improve production rates of asbestos-cementarticles from slow filtering asbestos fibers, inherent processlimitations have prevented either of these procedures from producingslurries or pastes that provide both rapid filtration and strongproducts.

- OBJECTS OF THE INVENTION Accordingly, it is an object of thisinvention to provide an effective procedure for greatly increasing thefiltration rate of slurries or pastes containing asbestos fiber, withouthaving the adverse effect on product strength that would result from asilicate treatment and most other known filtration-improving treatments.

Another object of this invention is to provide asbestos fibers whichpossess improved filtration characteristics for use in makingasbestos-cement products, and which do not result in lower strengthproducts as a direct result of the improved filterability properties ofthe fibers.

A further object of this invention is to provide a process for impartingto asbestos fibers desirable filtration properties while eliminating theloss in product strength that previously resulted from attempts todramatically increase filtration rates by silicate and other treatmentprocedures. I

These and other objects will be apparent to those skilled in the artfrom the description which follows and from the drawings.

SUMMARY OF THE INVENTION The invention provides a novel asbestos fiberproduct and a method of producing an asbestos fiber product thatpossesses desirable filtration characteristics for use in fabricatingasbestos-cement articles from slurries or pastes. The method comprisesapplying an aqueous solution of alkali metal silicate to asbestos fiberwhile maintaining the fiber in an air suspension to deposit on thesuspended fiber alkali metal silicate solids in amounts of at leastabout 0.4 percent by weight of the fiber, and subsequently depositing anonfoaming anionic dispersant on the fiber.

The combination treatment using alkali metal silicate and a non-foaminganionic dispersant is not only cumulative in its effect on thefiltration rate of asbestos fibers, but unexpectedly does not decreasethe strength of products made from the treated fibers as do fiberstreated with the same level of alkali metal silicate alone. The dualtreatment method of this invention permits usage of over 100 percentmore alkali metal silicate than the 0.4 0.6 percent by weight rangepreviously thought to be the commercially practicable upper limit. Forexample, chrysotile fibers treated with l percent sodium silicate, butno dispersant, possess improved filtration characteristics compared tountreated fibers, but asbestos-cement products made from suchsilicate-treated fibers are weaker than products made from untreatedfiber and are unsatisfactory from a strength standpoint.

On the other hand, fibers treated with 1 percent sodium silicate and anon-foaming anionic dispersant according to the dual treatment processof the present invention have filtration characteristics superior to the1 percent sodium silicate treated fibers, and also produce products thatpossess equal or superior strength characteristics when compared toproducts made from untreated fiber.

The invention dramatically increases production rates ofproducts from anasbestos-cement slurry or paste and eliminates the loss of strength inasbestos-cement products formed from the slurry or pastes which wouldotherwise result from inclusion of silicatetreated asbestos fibershaving more than about 0.4 0.6 percent by weight of silicate solidsdeposited on the fibers.

DETAILED DESCRIPTION OF THE INVENTION The process of treating asbestosfiber according to the method of this invention includes as a first stepthe application of alkali metal silicate to the surface of the asbestosfibers. An aqueous solution containing alkali metal silicate is sprayedonto the asbestos fibers while the fibers are maintained in a gaseoussuspension. This spray procedure has been found to be particularlydesirable for applying alkali metal silicates to asbestos fiber, if thefiber is to be subsequently packaged and transported or stored beforeuse.

The preferred procedure for depositing alkali metal silicates on theasbestos fibers is described in Pundsack et al. U.S. Pat. No. 3,173,831,assigned to the assignee of this invention. The disclosure of thePundsack et al. patent is incorporated herein by reference. In general,the spray technique disclosed by Pundsack et al. which comprises thepreferred first step in the present process involves the application ofa sprayable aqueous solution of alkali metal silicates consisting ofordinary commercial grades of sodium and/or potassium silicates havingalkali metal to silicate ratios ranging from about 1.60 to 3.75 mols SiOper mol of alkali metal. The silicate solution is applied in the form ofa finely divided atomized spray to the asbestos fibers. Although thepatent describes the concentration of alkali metal silicate in theaqueous solution as being in the range of about 3 percent to about 20percent by weight, it has been found in the present invention thatconsiderably higher concentrations can be used, such as, for example, 30percent and greater alkali metal silicate content.

While being sprayed, the fibers are maintained substantiallyindividually in an air or gaseous suspension such as the condition thatnormally exists in an asbestos fiberizer, such as a willow, or when thefibers pass through a fan or blower. Alkali metal silicate solutions ofthe above described concentrations can be effectively sprayed in afinely divided or atomized condition from typical commercial equipmentwithout clogging. The application of the silicate solutions as a finelydivided spray to fibers in vigorous motion permits the addition of largequantities of the aqueous solution without producing any visible wettingor cohering of the fiber.

Up to 15-20 percent of the aqueous silicate solution, based on fiberweight, can be sprayed on the air suspended fiber. The total amount ofsolution applied depends upon the concentration of the solution. Toproduce the beneficial effects of the present invention up to 4 percentby weight of the alkali metal silicate solids and preferably from about0.5 to about 2.0 percent by weight, is deposited on the fiber.

As discussed above, the application of alkali metal silicates to thesurface of asbestos fibers in quantities of at least about 0.4 percentby weight of the fiber, substantially improves the filtrationcharacteristics of the treated fiber when compared to untreated fiber.However, alkali metal silicate at these weight percentages has in thepast tended to considerably decrease the strength of productsincorporating the silicate-treated fiber.

In accordance with the invention, a non-foaming anionic dispersant isadded to silicate-treated asbestos fibers to dual treat the fibers. Thisresults in an increased filtration rate of slurries or pastes whichinclude the dual treated fibers above the filtration rate of slurries orpastes which include silicate-only treated fibers, and an increase inthe strength of asbestos-cement products formed from the dual treatedfibers above the strength of similar products formed from thesilicate-only treated fibers. By the addition of the nonfoaming anionicdispersant to the silicate treated fibers, the loss of strength whichwould otherwise result from the use of silicate-only treated fibers isdecreased.

The addition of the dispersant to the silicate-treated fibers can beaccomplished by numerous physical procedures. An aqueous solution of thedispersant can be sprayed on the silicate-treated fibers while they aresuspended using techniques similar to those described above for thesilicate treatment. The dispersant can also be added as a dry, finelydivided solid, and blown onto the silicate-treated asbestos fiber.

It has been found that a large number of non-foaming anionic dispersantsare effective to increase the filterability of asbestos-cement slurriesor pastes, and toy counteract the strength loss in asbestos-cementarticles which otherwise follows from a prior silicate treatment ofasbestos fibers. Preferred dispersants include a sodium salt ofcondensed naphthalene sulfonic acid such as marketed by Rohm and Haasunder the trade designation Tamol SN, hereinafter referred to at timesas simply Tamol, and a sodium ligno-sulfonate marketed by the Marathondivision of American Can Company under the trade designation MarasperseN-22; other suitable dispersants include a sulfonated benzimidazolderivative of a higher fatty acid marketed by Ciba Chemical and DyeCompany, Inc. under the trade designation Ultravon WC; a sugar-freecalcium lignosulfonate marketed by Lake States Yeast & ChemicalDivision, St. Regis Paper Company under the trade designation Toranil B;a sodium alkyl naphthalene sulfonate marketed by National AnilineDivision, Allied Chemical Corporation under the trade designationNaccolsol A; an alkyl aryl sodium sulfonate marketed by National AnilineDivision, Allied Chemical Corporation under the trade designationNaccotan A; a sodium salt of a condensed mononaphthalene sulfonatemarketed by Jacques Wolf and Company, Division of Nopco Chemical Companyunder the trade designation Lomar PW; a sodium salt of a condensednaphthalene sulfonate marketed by Jacques Wolf and Company, Division ofNopco Chemical Company under the trade designation Nopcosant; a sodiumsalt of polymerized alkyl naphthalene sulfonic acid marketed by Deweyand Almy Chemical Division, W. R. Grace and Company under the tradedesignation Darvan No. 1; sodium salts of polymerized substitutedbenzoid alkyl sulfonic acid marketed by Dewey and Almy ChemicalDivision, W. R. Grade and Company under the trade designation Darvan No.2; sodium salts of polymerized alkyl naphthalene sulfonic acid marketedby Dewey and Almy Chemical Division, W. R. Grace and Company under thetrade designation Darvan No. 15; a mono-calcium salt of polymerizedalkyl aryl sulfonic acids marketed by Dewey and Almy Chemical Division,W. R. Grace and Company under the trade designation Daxad No. 21; sodiumsalts of polymerized substituted benzoid alkyl sulfonic acids marketedby Dewey and Almy Chemical Division, W. R. Grace and Company under thetrade designation Daxad No. 23; sodium salts of substituted benzoidalkyl sulfonic acids and suspending'agent marketed by Dewey and AlmyChemical Division, W. R. Grace and Company under the trade designationDaxad No. 27; sodium salts of substituted benzoid alkyl sulfonic acidsand suspending agent marketed by Dewey and Almy Chemical Division, W. R.Grace and Company under the trade designation Darvan No. 3; and a groupcomprising sulfonated naphthalene formaldehyde polymers such as asulfonated condensate of naphthalene formaldehyde marketed by New YorkColor and Chemical Company, Division of American Dyewood, Inc. under thetrade designation Syntan NNC; a sodium salt of a sulfonatednaphthalene-formaldehyde condensate marketed by Dyestuff and ChemicalsDivision, General Aniline and Film Corporation under the tradedesignation Blancol; and a sodium salt of a sulfonatednaphthalene-formaldehyde condensate marketed by Dyestuff and ChemicalsDivision, General Aniline and Film Corporation under the tradedesignation Blancol N. The foregoing materials including Tamol andMarasperse are classified as dispersants in the publication: Detergentsand Emulsifiers, 1964 Annual, Copyright 1964 by John W. McCutcheon, Inc.

The non-foaming anionic dispersant added in the second step of this dualtreatment process is effective to produce advantageous results at verylow concentrations of from about 0.05 to 5.0 percent by weight based onthe dry weight of the asbestos fiber. Larger amounts of the non-foaminganionic dispersant can be used, but the added additional amounts aresuperfluous and do not produce any added advantages. Furthermore, as theamount of the dispersant is increased, it begins to act in its normallyintended manner as a dispersant and detrimentally affects the productionrate at which asbestos-cement articles can be produced. The amount ofdispersant used should not lower the surface tension of the asbestoscement slurry or paste below about 65 67 dynes/cm., as contrasted withthe surface tension of ordinary water of about 72 dynes/cm., thusfurther preventing any tendency for the slurry to foam. The preciseamount of the dispersant required to produce the desired results varieswith the percentage of the particulate solids in the slurry or paste inwhich the asbestos fiber is to be incorporated and the nature of theparticulate solids.

The asbestos fiber product produced by the abovedescribed processcomprises at least about 0.4 percent by weight silicate solids at leastpartially coating the surface of the asbestos fibers, and a non-foaminganionic dispersant distributed as a coating on the surface of thesilicate-coated fibers. The fiber product can be compressed duringpackaging operations and retains its ability to improve production ratesand to produce strong asbestos cement articles through shipment andprolonged storage periods.

In a preferred embodiment of the present invention, chrysotile asbestosfibers are first coated by spraying an aqueous solution of sodiumsilicate onto the fibers to deposit about 0.75 percent by weight ofsilicate solids and the fibers are then coated withabout 0.4 percent byweight of the non-foaming anionic dispersant, such as Tamol.

Portland cement is the principal hydraulic cementitious material used incarrying out the new method of preparing asbestos'cement structures inaccordance with the invention. However, use of other hydraulic cements,e.g., pozzolanic cement, calcium aluminate cement and calcium sulphatecement, can be used, if desired, to replace at least part of thePortland cement.

Suitable asbestos-cement structures can be prepared using mixturesconsisting essentially of the cement and asbestos fibers. However, it isoften desirable from a viewpoint of cost, as well as structuralproperties of the final products, to include additional siliceousmaterials in the aqueous slurries and pastes so that they willconstitute a part of the ultimate shaped structures. Consequently, sand,powdered silica, ground mica, ground feldspar and the like can bepresent in the slurry or paste.

The following examples are presented to provide a more completeunderstanding of the invention. The specific techniques, conditions,materials and/or proportions set forth are exemplary and should not beconstrued as limiting the scope of the invention. All percentages listedin this application are weight percentages unless stated to beotherwise.

EXAMPLES 1-4 A chrysotile asbestos fiber mined in Quebec, Canada istreated in accordance with the dual treatment process of the invention.The filtration characteristics of the resulting fiber are compared withuntreated fiber and fiber treated with only silicate in Table l below.

An atomized 30 percent solution is sprayed on the tested fibers whilethe fibers are being transported in an air stream. The dispersant, asodium salt of condensed naphthalene sulfonic acid (Tamol) in the drypowder form, is blown into the cyclone which is used to collect thesilicate treated fibers and is distributed as a coating on the silicatetreated fibers.

The treated fibers are tested for their Fiberator Index value, whichresults from a standard Johns-Manville Corporation filtration test whichis used to determine the production rate properties of a fiber for usein wet machine operations. It is different in concept from a wetpermeability test which merely measures the time elapsed for a givenportion of liquid to pass through a filter mat, or established filtercake.

The Fiberator lndex value is an empirical value obtained using a testapparatus comprising an open topped vessel having a side inlet opening,a side outlet opening, a bottom outlet and a screen covering the bottomoutlet. A filtrate-collection flask connected to a vacuum source isconnected to the bottom outlet of the vessel to permit drawing a vacuumon a filter cake formed on the screen.

ln the test procedure, an aqueous asbestos-cement slurry is flowedthrough the vessel and particles in the slurry build up to form a filtercake on the screen. Vacuum pulls water through the cake of built-upmaterial on the screen and into the collection flask.

The quantity of water gathered in the collection flask in a given periodof time is measured as is the thickness of the material that builds upon the screen. The milliliters of collected water is multiplied by afactor of 0.0833, and the dry weight in grams of the material collectedby the screen is multiplied by a factor of 4.0. The average value of theproducts of these multiplication operations is the Fiberator lndex. Itis an empirical (QAMA) grading system.

TABLE I Example Fiber Treatment Fiberator Index I (No Treatment) 51 2(0.5% Silicate) 59 3 (1% Silicate) 78 4 (1% Silicate +0.37% Tamol) 87Comparing the results of Example 4, which includes fibers treated inaccordance with the invention, with the results of the other examplesshows that one index of filter-ability is increased by the dualtreatment process of this invention.

EXAMPLES 5-8 in these examples, chrysotile asbestos fibers, whileair-suspended, are initially sprayed with a 20 percent aqueous solutionof sodium silicate solids to deposit 1 percent by weight of silicatesolids on the fibers. Subsequently, 0.4 percent by weight of Tamol isapplied to the fibers either by blowing dry powder into the cyclone usedto collect the silicate-treated fibers prior to packaging, or byrecycling the silicate-treated fibers past the zone used to initiallyspray on the silicate, and spraying an aqueous solution of Tamol ontothe silicate-treated fibers. These fibers are compared with untreatedfibers and fibers treated only with 1 percent silicate. The weightpercentages expressed above are based on the weight of untreatedasbestos fiber.

The fibers are incorporated in a 7 percent solids slurry of the typecommonly used in making asbestos cement pipe and processed on a smallwet machine-The solids in the slurry comprise approximately 20 percentfiber, 32 percent silica, and 48 percent Portland cement.

The's'mall wet machine is a conventional board-making type of machinehaving a mixing tank wherein a slurry, comprising asbestos fibers,hydraulic cement and silica as the particulate material is prepared. Thesolids forming the-slurry are filtered onto a cylinder mold in a vat andtransferred as a continous layer or filter mat onto a felt which carriesthe layer to an accumulator roll where the layer is rolled into aplurality of laminations. When the desired number of laminations havebeen formed on the accumulator roll, a longitudinal cut is made and thelaminated layers are removed from the accumulator roll as a unitarysheet which is then pressed and subjected to conventional asbestoscementcuring operations.

The products are then tested to determine their strength properties andthe production rates are noted.

Table Il below lists the results of these tests.

TABLE II Example 5 6 7 8 Weight Silicate (basis fiber) 1% None 1% 1%Weight Tamol dox.

9 (basis fiber) None None 0.4% 0.4% Fiberator lndex 56 53 69 74 Modulusof Rupture (Kg/cm) 460.7 506.4 535.4 499.4 Density (gm/cc) 1.774 1.7511.778 1.754 Thickness (mm) 5.85 4.703 7.76 7.70 Production Rate (lb.Product per hr. per ft. of Product width 301 239 400 392 Comments TamolTamol added as added by a dry spraying powder as an aqueous solution Inanalyzing the results of Examples -8, it is apparent from Examples 5 and6 that a 1 percent silicate treatment by itself increased the productionrate from 239 for an untreated fiber to 301 (in the units stated in thetable), but the strength of the asbestos-cement pipe produced from thesefibers decreased considerably from a modulus of rupture of 506.4 to460.7 kg/cm 1n contradistinction, however, Examples 7 and 8 show thatthe dual treated fibers of the present invention possess a desirablecombination of superior filtration characteristics and the ability toproduce strong asbestos-cement products. As is apparent from Example 8,the addition of only 0.4 percent Tamol added as a spray of an aqueoussolution upgraded the strength the 1 percent silicate treated fibersfrom 460.7 to 499.4 Kglcm almost to the level of the untreated fibers(506.4), and yet the dual treated fibers were able to vastly improveproduction rates for asbestos-cement pipe to 392 from 239 for theuntreated fibers and from 301 for the silicate treated fibers. Example 7shows that even more surprising results can be obtained by adding 0.4percent Tamol as a dry powder to fibers previously treated with 1percent silicate. The use of such dual treated fibers produced thehighest production rate (400), considerably above those of the untreatedor 1 percent silicate treated fibers. Moreover, the strength of theasbestos-cement pipe formed from these dual treated fibers improved to alevel above that of pipe formed from the untreated fibers (535.4 vs.506.4 Kg/cm) and much above that of pipe formed from 1 percent silicatedtreated pipe. It can be concluded that by following the teachings ofthis invention, higher production rates can be accomplished withminimized loss in strength in the final product and in some cases withincreased strength over products formed from untreated fibers.

In addition to the use of alkali metal silicate, col loidal silica canalso be used in the present invention in the same amounts as thesilicate to produce silica coated fibers. Such material would be appliedin the same manner, as by spraying, and would be introduced in the formof suspended colloidal silica. An example of suitable material is thatsold under the trademark Lult is to be understood that variations andmodifications of the present invention may be made without departingfrom the spirit of the invention. It is also to be understood that thescope of the invention is not to be interpreted as limited to thespecific embodiment disclosed herein, but only in accordance with theappended claims when read in the light of the foregoing disclosure.

Iclaim: 1. An asbestos fiber product having improved filtration and goodstrength characteristics and capable of being packaged and stored,comprising: chrysotile asbestos fibers at least partially coated with atleast about 0.4 percent by weight of material selected from the groupconsisting of alkali metal silicate solids, silica and mixtures thereof,and having a non-foaming anionic sulfonated dispersant distributed onthe surface of the coated fibers.

2. The product of claim 1 including up to about 2 percent by weight,based on the weight of the fiber, of alkali metal silicate solids andfrom about 0.05 to about 5.0 percent by weight based on the weight ofthe fiber 1 of a non-foaming anionic sulfonated dispersant.

3. The product of claim 2 in which the dispersant comprises a sodiumsalt of condensed naphthalene sulfonic acid.

4. A process for producing an asbestos fiber product that possessesimproved filtration characteristics and improving the production rate ofasbestos cement articles without decreasing the strength of sucharticles comprising: applying a spray comprising material selected fromthe group consisting of an aqueous solution of alkali metal silicate,suspended colloidal silica and mixtures thereof, to asbestos fiber whilemaintaining the fiber in an air suspension to deposit at least about 0.4percent by weight of solids on the airsuspended fibers, and subsequentlyadding a non-foam ing anionic sulfonated dispersant to the fiber todistribute said dispersant on said fibers.

5. The process of claim 1 in which the non-foaming anionic sulfonateddispersant is added to the fiber as a dry powder.

6. The process of claim 1 in which the non-foaming anionic sulfonateddispersant is placed in an aqueo'us olution and sprayed on'the fiber.

- 7. The process of claim 1 in which the anionic sulfonated dispersantis added in amounts from about 0.05 to about 5.0 percent by weight basedon the weight of the asbestos fiber.

8. The process of claim 7 in which the sulfonic acid derivative is asodium salt of condensed naphthalene sulfonic acid.

9. The process of claim 1 in which the alkali metal silicate is selectedfrom the group consisting of sodium and potassium silicates and mixturesthereof.

10. The process of claim 9 including depositing from about 0.5 to about2 percent by weight of alkali metal silicate solids on the fibers.

1. An asbestos fiber product having improved filtration and goodstrength characteristics and capable of being packaged and stored,comprising: chrysotile asbestos fibers at least partially coated with atleast about 0.4 percent by weight of material selected from the groupconsisting of alkali metal silicate solids, silica and mixtures thereof,and having a non-foaming anionic sulfonated dispersant distributed onthe surface of the coated fibers.
 2. The product of claim 1 including upto about 2 percent by weight, based on the weight of the fiber, ofalkali metal silicate solids and from about 0.05 to about 5.0 percent byweight based on the weight of the fiber of a non-foaming anionicsulfonated dispersant.
 3. The product of claim 2 in which the dispersantcomprises a sodium salt of condensed naphthalene sulfonic acid.
 4. Aprocess for producing an asbestos fiber product that possesses improvedfiltration characteristics and improving the production rate of asbestoscement articles without decreasing the strength of such articlescomprising: applying a spray comprising material selected from the groupconsisting of an aqueous solution of alkali metal silicate, suspendedcolloidal silica and mixtures thereof, to asbestos fiber whilemaintaining the fiber in an air suspension to deposit at least about 0.4percent by weight of solids on the air-suspended fibers, andsubsequently adding a non-foaming anionic sulfonated dispersant to thefiber to distribute said dispersant on said fibers.
 5. The process ofclaim 1 in which the non-foaming anionic sulfonated dispersant is addedto the fiber as a dry powder.
 6. The process of claim 1 in which thenon-foaming anionic sulfonated dispersant is placed in an aqueoussolution and sprayed on the fiber.
 7. The process of claim 1 in whichthe anionic sulfonated dispersant is added in amounts from about 0.05 toabout 5.0 percent by weight based on the weight of the asbestos fiber.8. The process of claim 7 in which the sulfonic acid derivative is asodium salt of condensed naphthalene sulfonic acid.
 9. The process ofclaim 1 in which the alkali metal silicate is selected from the groupconsisting of sodium and potassium silicates and mixtures thereof.